The long-term objective of the proposed research is to develop new methods for the synthesis of seven and eight membered heterocycles. The development of new methods for the conversion of simple organic starting materials to complex products remains a central theme of research in organic chemistry. The application of new chemical transformations to the synthesis of biologically active natural products or pharmaceuticals can serve to shorten synthetic routes, and make such compounds more readily available to the public. The short-term objective is to investigate intramolecular Hetero Diels-Alder (HDA) reactions in which cyclobutadiene (protected as an iron tricarbonyl complex) is the 4pi component. Dienophiles to be studied will include aldehydes, ketones, imines, and thioketones. Exploratory reactions will be carried out to probe the effect of the nature of the tether (length and composition), and the substitution pattern on the dienophile, on the HDA reaction. Using methodology previously developed in the Snapper group, the tricyclic 5-4-4 skeleton obtained in the HDA reaction can be converted into the 5-8, 5-8-5, or 5-7 ring systems, which are found in a number of natural products.